Colle San Magno is a comune (municipality) in the Province of Frosinone in the Italian region Lazio, located about 110 km southeast of Rome and about 30 km southeast of Frosinone.
Its name refers to St. Magnus of Anagni. The town was founded in the 11th century, and it was later ruled by the D'Avalos and, from the 16th century, by the Boncompagni. In 1796 it was acquired by the Kingdom of Naples.
Attractions include the medieval castle, the old asphalt mines and the church of S.M. Assunta.